Micro-machined ultrasonic transducer (MUT) arrays have their structure and fabrication technology fundamentally different to those of thickness mode piezoelectric transducers. Their performance needs to be modelled and optimized before MEMS fabrication process is engaged. A 3-dimentional finite element modeling (3-D FEM) analysis is established for the simulation of a 2-D 7×7 piezoelectric micromachined ultrasonic transducer (PMUT) array in its cavity and buffer structure. The main characteristics and parameters of the PMUT are calculated in frequency domain, in terms of the electrical impedance, resonant modes patterns, stress distribution, and in particular the cross talk between array elements, The method provides an efficient tool for the design and optimization of PMUT structures. A novel structure with double active layers PMUT is proposed and simulated with the FEM.